The present invention relates to a system for distributing electric power, particularly systems for low and medium voltage which comprise automatic protection breakers.
More specifically, the invention relates to a distribution system which comprises automatic protection breakers which are distributed hierarchically on various levels. The invention further comprises a method for controlling the intervention sequence of the automatic breakers, which are mutually interlocked so as to intervene selectively in order to cut out the faulty parts of the system.
These distribution systems are currently protected by means of automatic breakers, in which protection against a short-circuit fault with current values close to the breaking capacity is provided by means of classical electromechanical devices based on the electrodynamic effect of fault currents, which have a reaction time on the order of milliseconds.
Electric power distribution grids have a plurality of said breakers, which are distributed radially on various levels in order to selectively limit the power outage to the part or region of the network affected by the fault.
This selectivity among the various breakers is currently achieved by utilizing the different values of the current and of the intervention times of the protection devices and their different mechanical inertia, which depends on their size (and therefore on the masses involved in the opening movement).
In other words, a breaker to which several other breakers supplying an equal number of loads or subsections of the system are connected has higher settings for the protection device, is larger and has greater inertia than the breakers that it supplies, and therefore does not intervene in case of a fault downstream of the smaller breakers that it supplies. This of course occurs for all the higher levels to which the fault current can propagate.
The size of the breakers is in turn a function of the nominal current of the breaker, and therefore the size allocation of the system, by having to ensure the selectivity requirements, is based not only on the values of the working currents that are present in each node but also on the selectivity requirements, which often require to keep the short-circuit current in the system for longer than actually necessary to interrupt the fault current.
While the need to minimize the fault energy, i.e., damage, requires the fastest possible intervention, the need to select among the breakers the one that must intervene in fact entails slowing the protective intervention. Accordingly, the conventional systems of the prior art do not allow to optimize the size allocation of an electric power distribution system as regards the protection breakers.